Better overall diet quality was related to larger total brain volume, gray matter, white matter, and hippocampal volume, according to Meike Vernooij, MD, PhD, of the Erasmus University Medical Center in Rotterdam, and colleagues.

These associations were driven by several food groups -- vegetables, fruit, nuts, whole grains, dairy, and fish -- which contributed differentially to the effect on brain changes, they reported in Neurology.

"People with greater brain volume have been shown in other studies to have better cognitive abilities, so initiatives that help improve diet quality may be a good strategy to maintain thinking skills in older adults," Vernooij said in a statement. "More research is needed to confirm these results and to examine the pathways through which diet can affect the brain."

"There is increasing evidence that a healthy diet supports brain cellular aging, with positive effects on cognition," said Lisa Mosconi, PhD, of Weill Cornell Medical College in New York, who was not involved in the study. "A large body of literature has shown that cognitively intact elderly and middle-aged people who follow healthy diets, such as the Mediterranean diet, have lower risk of cognitive decline and dementia later in life," she told MedPage Today.

While most of these studies have looked at diet and cognitive outcomes, few have assessed food intake and brain structure.

For this research, researchers evaluated 4,213 participants from the Rotterdam Study, a population-based community-dwelling cohort in the Netherlands, who did not have dementia or cortical infarcts. Participants had an average age of 65.7; 56.8% were female. They completed questionnaires about their frequency of eating and serving sizes of 389 food items and had MRI brain scans from 2005 to 2015.

The researchers evaluated adherence to 14 items in the Dutch dietary guidelines: vegetables, fruit, whole grain products, legumes, nuts, dairy, fish, tea, whole grains products, unsaturated fats and oils of total fats, red and processed meat, sugary beverages, alcohol, and salt. They calculated an overall diet score (0 to 14) reflecting adherence to the dietary guidelines by adding scores for these food groups. They also calculated a Mediterranean diet score based on median food intake of the study population.

Overall, participants had a median dietary guideline adherence score of 7 (on a theoretical range of 0 to 14) and a mean total brain volume of 932.01 mL.

Adjusting for other cardiovascular risk factors did not change the trend, and diet was not linked to brain white matter lesions or small brain bleeds. Effect estimates of the association between the Mediterranean diet score and brain volume were similar to the Dutch findings.

This is not surprising, observed Mosconi, whose research team recently showed that over a span of 3 years, middle-aged individuals who had low adherence to a Mediterranean-style diet had increases in Alzheimer's plaque deposition and reductions in brain activity compared with people who had higher adherence. A high Dutch diet quality score "exhibits similar characteristics to a Mediterranean-style diet, though adjusted for Northern European dietary habits -- meaning it has overall higher percentage of fat," she said.

There is much confusion around diet and brain health and it's up to doctors to provide clarity, Mosconi added: "One day people are told they should go vegan; the next day they can't touch bread."

"The scientific literature thus far indicates that a balanced diet pattern rich in healthy carbs and fiber, with low-to-moderate fat content, is supportive of brain aging," she said. "There is no evidence for the opposite, which provides a strong argument in favor of recommending a Mediterranean-style diet for brain aging and dementia prevention."

Several mechanisms might account for associations between diet and brain health, Vernooij and coauthors noted. Nutrition could have a direct effect on neuronal health or could influence vascular risk or cerebrovascular disease. Additionally, "we might be looking at an effect of neurodevelopment where variations in diet quality throughout life have different effects on brain structure and brain health," they wrote.

The Rotterdam study shows only an association, not cause and effect, Vernooij said, and is limited by self-reported dietary data. It was conducted in a Dutch population and other groups may not have similar results.

Tis study was funded by Erasmus Medical Center and Erasmus University, Netherlands Organization for Health Research and Development (ZonMw), the Research Institute for Diseases in the Elderly (RIDE), the Ministry of Education, Culture and Science, the Ministry of Health, Welfare and Sports, the European Commission (DG XII), and the Municipality of Rotterdam.

Vernooij reported no disclosures relevant to the manuscript. Other researchers reported relationships with Nestle and Metagenics.

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